Myopia, also known as short-sightedness, is a refractive condition of the eye where light from distant objects is focussed in front of the retina. This condition causes distant objects to be perceived blurred by the viewer. Myopia is often first noticed in children at school age and may increase in severity until young adulthood. This phenomenon is often referred to as myopia progression.
The distance vision of people with myopia has been corrected with conventional single-vision lenses, which focus the light from distant objects onto the central retina, the fovea, and thus bring the distant objects clearly into focus.
In recent years, there has been increased interest in the peripheral optics of the eye, due to findings that peripheral refractive errors are associated with refractive error development. Studies on monkeys (Smith et al.) have shown that the peripheral retina can mediate emmetropising responses. Devices and methods for utilising the findings of these studies are described in U.S. Pat. No. 7,503,655 B2 (Smith et al.), the entire content of which is incorporated herein by reference. Several such correction devices, including spectacle lenses and contact lenses, have been designed, some of which have been manufactured and tested in clinical trials (Sankaridurg et al. OVS 2010). The study by Sankaridurg et al. showed a 30% reduction in myopia progression in Chinese children, aged 6-12 years with at least one myopic parent when the children wore spectacle lenses that were designed with the aim to provide clear central vision for distance and reduce peripheral hyperopic defocus.
When focussing on objects at near, myopic eyes may experience accommodative lag i.e. the image is behind the retina and thus the eye experiences hyperopic defocus (blur). Studies have found that there is a correlation between lag of accommodation and progression of myopia. Use of simultaneous vision lenses in the form of bifocal spectacles and in the form of progressive addition spectacles with an ADD power (relative plus compared to distance power, the refractive power of the distance point) reduce the accommodative demand at near and have been prescribed to children with the aim of inhibiting myopia progression. These simultaneous vision lenses are based on central refractive errors and do not take into account the peripheral refractive error profile at near.
A study by Whatham et al. (JOV, 2009) measured peripheral refraction in young myopic adults and found that when viewing near distances i.e. with accommodative effort, the peripheral refractive errors (spherical equivalent, M) became progressively and significantly (p<0.001) more myopic/less hyperopic relative to central refractive error. The relative change in refractive error between distance and near in Whatham et al.'s myopic participant group was about +0.8 D at 40 degrees nasal retina and about +0.2 D at 40 degrees temporal retina.
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